Intel Atom Processor N450, D410 and D510 for Embedded Applications

Transcription

1 Intel Atom Processor N450, D410 and D510 for Embedded Applications Thermal Design Guide February 2010 Revision 1.0 Document Number: EN

2 INFORMATION IN THIS DOCUMENT IS PROVIDED IN CONNECTION WITH INTEL PRODUCTS. NO LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT. EXCEPT AS PROVIDED IN INTEL S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, INTEL ASSUMES NO LIABILITY WHATSOEVER, AND INTEL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY, RELATING TO SALE AND/OR USE OF INTEL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR PURPOSE, MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT. Intel products are not intended for use in medical, life saving, or life sustaining applications. Intel may make changes to specifications and product descriptions at any time, without notice. Designers must not rely on the absence or characteristics of any features or instructions marked "reserved" or "undefined." Intel reserves these for future definition and shall have no responsibility whatsoever for conflicts or incompatibilities arising from future changes to them. The information here is subject to change without notice. Do not finalize a design with this information. The products described in this document may contain design defects or errors known as errata which may cause the product to deviate from published specifications. Current characterized errata are available on request. This document contains information on products in the design phase of development. Hyper-Threading Technology requires a computer system with a processor supporting HT Technology and an HT Technology enabled chipset, BIOS and operating system. Performance will vary depending on the specific hardware and software you use. For more information including details on which processors support HT Technology, see Intel and the Intel logo are trademarks of Intel Corporation in the U.S. and other countries. *Other names and brands may be claimed as the property of others. Copyright 2010, Intel Corporation. All rights reserved. 2 Thermal Design Guide

3 Contents 1 Introduction Reference Documents Terminology Package Information Thermal Design Power Package Mechanical Requirements Processor Thermal Features Processor Power Dissipation Thermal Monitor Implementation Thermal Monitor PROCHOT # Signal Thermal Control Circuit Operation and Configuration On-Demand Mode System Consideration Operating System and Application Software THERMTRIP# Signal Cooling System Failure Warning Digital Thermal Sensor Thermal Diode Thermal Solution Requirement Characterizing the Thermal Solution Requirement Example: Calculating the Required Thermal Performance Reference Thermal Solution Thermal Solution Design Considerations Thermal Solution Design Factors Natural Convection Heatsink Experimental Test Setup Mechanical Design Fanless System Design Examples System Level Simulations for Print Imaging System Level Simulations for Industrial PC Reference Heatsink for Forced Convection Active Heatsink Keep Out Zone Requirements Thermal Metrology Digital Thermal Sensor measurement (TJUNCTION- MAX Methodology) Local Ambient Temperature Measurement Guidelines Appendix A: Thermal Solution component supplier Thermal Design Guide 3

4 Appendix B: Mechanical Drawings B.1: Mini ITX Forced Convection Heatsink Assembly (40 x 40 mm) B.2: Mini ITX Forced Convection Heatsink Drawing B.3: PCB Keep-Out Zone for Forced Convection Heatsink B.4: Mini-ITX Natural Convection Heatsink Assembly (64 x 64 mm) B.5: Mini-ITX Natural Convection Heatsink drawing B.6: PCB Keep- Out Zone for Natural Convection Heatsink Figures Figure 1. Intel Atom Processor D510 micro-fcbga Package...8 Figure 2. Intel Atom Processor N450 and D410 micro-fcbga Package...9 Figure 3. Thermal Monitor 2 Frequency and Voltage Ordering Figure 4. Concept of Clocks under Thermal Monitor Control Figure 5. Processor Thermal Characterization Parameter Relationships Figure 6. Isometric View of Natural Convection Test Chamber Figure 7. Mini-ITX Natural Convection Reference Heatsink Assembly (Natural Convection) Intel part # E Figure 8. Model setup Figure 9. Isometric view of model setup Figure 10. Natural Convection Airflow Plot for Vertical Chassis Configuration Figure 11. Isometric view of horizontal orientation Figure 12. Natural Convection Airflow Plot for Horizontal Chassis Configuration Figure 13 Vertical Fanless system for Industrial PC Figure 14. Direct Chassis Conduction for Industrial PC: simplified drawing for gap pad and heat spreader stackup for ICH8M Figure 15. Isometric view of Inductrial PC simulation Figure 16. Natural Convection Airflow plot for Vertical Chassis Configuration Figure 17. Mini ITX Forced Convection Reference Thermal Solution Assembly Figure 18. Mini-ITX Forced Convection Reference Heatsink Thermal Performance versus Airflow Rate Figure 19. Mini-ITX Active Heatsink Figure 20. Locations for measuring T LA with Active heatsink Figure 21. Locations for Measuring T LA, Passive Heatsink Tables Table 1. Thermal Specification Table 2. Processor Loading Specification Table 3. Thermal Diode Interface Table 4. Thermal Diode Parameters using Transistor Model Table 5. Required Thermal Solution Performance (Ψ JA ) Table 6. Experimental Thermal Solution Performance for 64 x 64mm Heatsink (Intel part # E ) Table 7. Experimental Thermal Solution Performance for 40 x 40 mm Heatsink (Intel part# E ) Table 8. Experimental Thermal Solution Performance for Active Heatsink (Intel part# E ) Table 9. Suppliers Thermal Design Guide

5 Introduction 1 Introduction This document describes the thermal characteristics of the Intel Atom Processor N450, D410 and D510 and provides guidelines for meeting the thermal requirements imposed on a single-processor system. The goals of this document are to: Identify the thermal and mechanical specification for the device Describe a reference thermal solution that meets the specifications A properly designed thermal solution adequately cools the device die temperature at or below the thermal specification. This is accomplished by providing a suitable local ambient temperature, ensuring adequate local airflow, and minimizing the die to local ambient thermal resistance. Operation outside the functional limits can degrade system performance and may cause permanent changes in the operating characteristics of the component. This document describes thermal and mechanical design guidelines for the Intel Atom processors in the micro Flip Chip Ball Grid Array (micro-fcbga) package. For thermal design information on other Intel components, refer to the respective component datasheets. 1.1 Reference Documents Document Intel ICH8 Family Datasheet Intel Atom Processor D400 and D500, Thermal Mechanical Specifications and Design Guideline Document No./Location asheet/ pdf See Note 1 Intel Atom Processor (Pineview) Thermal Model User s Guide See Note 1 Intel Atom Processor N450 and Intel Atom Processor D410 See Note 1 Desktop SKUs: Intel Atom Processor D400 and D500 Datasheet Volume 1 and 2 Mobile SKUs: Intel Atom Processor N400 Datasheet Volume 1 and 2 See Note 1 See Note 1 Note: 1. For the latest revision and order number of this document, contact your Intel field sales representative. Thermal Design Guide 5

6 Introduction 1.2 Terminology Term Description C Degrees Celsius EDS FCBGA in. PCB T J-MAX T J-MIN T J External Design Specification Flip Chip Ball Grid Array Inches Printed Circuit Board The maximum junction temperature of the processor, as specified in the processor datasheet ( C) The minimum junction temperature of the processor, as specified in the processor datasheet ( C) Junction Temperature of Processor T LA T S TIM TDP W Ψ JS Ψ SA Ψ JA Local ambient temperature ( C). This is the temperature measured inside the chassis, approximately 1 upstream from a component heatsink. Heatsink Temperature measured at geometric center of heatsink base. Thermal Interface Material the thermally conductive compound between the heatsink and processor. This material fills air gaps and voids, and enhances spreading of the heat from the processor to the heatsink. Thermal Design Power Watt Junction-to-sink thermal characterization parameter. Defined as (T J T S ) / TDP Sink-to-ambient thermal characterization parameter. Defined as (T S T LA ) / TDP Junction-to-ambient thermal characterization parameter. Defined as (T J-MAX T LA ) / TDP 6 Thermal Design Guide

7 Package Information 2 Package Information The Intel Atom Processor N450, D410 and D450 all utilize a 22 x 22 mm, 559 ball micro- FCBGA package as shown in Figure 1 and Figure 2. Note that there are capacitors near the die. Although the die-side capacitors are slightly shorter than the silicon die, be careful to avoid contacting the capacitors with electrically conductive materials or a heatsink base. Consider using an insulating material between the capacitors and heatsink to prevent capacitor shorting. The data provided in this section is for reference purposes only. Refer to the device s most recent datasheet for up-to-date information. In the event of conflict, the device s datasheet supersedes data shown in these figures. Thermal Design Guide 7

8 Package Information Figure 1. Intel Atom Processor D510 micro-fcbga Package 8 Thermal Design Guide

9 Package Information Figure 2. Intel Atom Processor N450 and D410 micro-fcbga Package Thermal Design Guide 9

10 Package Information 2.1 Thermal Design Power Thermal Design Power (TDP) specifications for the Intel Atom processors N450, D410 and D510 are listed in Table 1. TDP is the recommended design point for the thermal solution s power dissipation and is based on running worst-case, real-world applications and benchmarks at maximum component temperature. The thermal solution must ensure that the processor junction temperature limit is never exceeded under TDP conditions. Table 1. Thermal Specification CPU SKU # of Cores Frequency (GHz) TDP (W) T J-MAX ( C) T J-MIN ( C) Die Size (cm 2 ) Intel Atom Processor N450 Intel Atom Processor D410 Intel Atom Processor D Package Mechanical Requirements The processor package has mechanical load limits, maximum static and dynamic load limits, which should not be exceeded during their respective stress conditions. These include heat-sink installation, removal, mechanical stress testing, and standard shipping conditions. When a compressive static load is necessary to ensure thermal performance of the thermal interface material between the heat-sink base and the processor die, it should not exceed the corresponding specification. When a compressive static load is necessary to ensure mechanical performance, it should remain in the minimum/maximum range specified. No portion of the substrate should be used as a mechanical reference or loadbearing surface for the thermal or mechanical solution. Table 2. Processor Loading Specification Parameter Minimum Maximum Notes Static Compressive Load 24N [5.4 lbf] 67N [15 lbf] 1, 2, 3 NOTES: 1. These specifications apply to uniform compressive loading in a direction normal to the processor die. 2. This is the minimum and maximum static force that can be applied by the heat-sink and retention solution to maintain the heat-sink and processor interface. 3. These specifications are based on limited testing for design characterization. Loading limits are for the package only. 4. Processor loading specifications are for dual and single core. 10 Thermal Design Guide

11 Processor Thermal Features 3 Processor Thermal Features 3.1 Processor Power Dissipation An increase in processor operating frequency not only increases system performance, but also increases the processor power dissipation. The relationship between frequency and power is generalized in the following equation: P = CV 2 F (where P = power, C = capacitance, V = voltage, F = frequency) From this equation, it is evident that power increases linearly with frequency and with the square of voltage. In the absence of power saving technologies, ever increasing frequencies will result in processors with power dissipations in the hundreds of watts. Fortunately, there are numerous ways to reduce the power consumption of a processor, and Intel is aggressively pursuing low power design techniques. For example, decreasing the operating voltage, reducing unnecessary transistor activity, and using more power efficient circuits can significantly reduce processor power consumption. An on-die thermal management feature called Thermal Monitor is available on the processor. It provides a thermal management approach to support the continued increases in processor frequency and performance. By using a highly accurate on-die temperature sensing circuit and a fast acting Thermal Control Circuit (TCC), the processor can rapidly initiate thermal management control. The Thermal Monitor can reduce cooling solution cost, by allowing thermal designs to target TDP. 3.2 Thermal Monitor Implementation The Thermal Monitor helps control the processor temperature by activating the TCC (Thermal Control Circuit) when the processor silicon reaches its maximum operating temperature. The temperature at which the Intel Thermal Monitor activates the TCC is not user configurable. Bus traffic is snooped in the normal manner and interrupt requests are latched (and serviced during the time that the clocks are on) while the TCC is active. With a properly designed and characterized thermal solution, it is anticipated that the TCC would only be activated for very short periods of time when running the most power intensive applications. The processor performance impact due to these brief periods of TCC activation is expected to be minor and hence not detectable. An under designed thermal solution that is not able to prevent excessive activation of the TCC in the anticipated ambient environment may cause a noticeable performance loss and may affect the long-term reliability of the processor. In addition, a thermal solution that is significantly under designed may not be capable of cooling the processor even when the TCC is active continuously. The Intel Thermal Monitor controls the processor temperature by modulating (starting and stopping) the processor core clocks when the processor silicon reaches its maximum operating temperature. The Intel Thermal Monitor uses two modes to activate the TCC: automatic mode and on-demand mode. If both modes are activated, automatic Thermal Design Guide 11

12 Processor Thermal Features mode takes precedence. There is only one automatic mode called Intel Thermal Monitor 1 (TM1). This mode is selected by writing values to the MSRs of the processor. After automatic mode is enabled, the TCC will be activated only when the internal die temperature reaches the maximum allowed value for operation. The Intel Thermal Monitor automatic mode must be enabled through BIOS for the processor to be operating within specifications. Intel recommends TM1 be enabled on Intel Atom processors. When TM1 is enabled and a high temperature situation exists, the clocks will be modulated by alternately turning the clocks off and on at a 50% duty cycle. Cycle times are processor speed dependent and will decrease linearly as processor core frequencies increase. Once the temperature has returned to a non-critical level, modulation ceases and TCC goes inactive. A small amount of hysteresis has been included to prevent rapid active/inactive transitions of the TCC when the processor temperature is near the trip point. The duty cycle is factory configured and cannot be modified. Also, the automatic mode does not require any additional hardware, software drivers, or interrupt handling routines. Processor performance will be decreased by the same amount as the duty cycle when the TCC is active. The Intel Thermal Monitor automatic mode must be enabled through the BIOS for the processor to be operating within specifications. Intel recommends TM1 be enabled on the processors. TM1 feature can be referred to as Adaptive Thermal Monitoring features. The TCC may also be activated via on-demand mode. If bit 4 of the ACPI Intel Thermal Monitor control register is written to a 1, the TCC will be activated immediately independent of the processor temperature. When using the on-demand mode to activate the TCC, the duty cycle of the clock modulation is programmable via bits 3:1 of the same ACPI Intel Thermal Monitor control register. In automatic mode, the duty cycle is fixed at 50% on, 50% off, however in on-demand mode, the duty cycle can be programmed from 12.5% on/ 87.5% off, to 87.5% on/12.5% off in 12.5% increments. On-demand mode may be used at the same time automatic mode is enabled, however, if the system tries to enable the TCC via on-demand mode at the same time automatic mode is enabled and a high temperature condition exists, automatic mode will take precedence. An external signal, PROCHOT# (processor hot) is asserted when the processor detects that its temperature is above the thermal trip point. Bus snooping and interrupt latching are also active while the TCC is active. Besides the thermal sensor and thermal control circuit, the Intel Thermal Monitor also includes one ACPI register, one performance counter register, three MSR, and one I/O pin (PROCHOT#). All are available to monitor and control the state of the Intel Thermal Monitor feature. The Intel Thermal Monitor can be configured to generate an interrupt upon the assertion or de-assertion of PROCHOT#. PROCHOT# will not be asserted when the processor is in the Stop Grant power states; hence, the thermal diode reading must be used as a safeguard to maintain the processor junction temperature within maximum specification. If the platform thermal solution is not able to maintain the processor junction temperature within the maximum specification, the system must initiate an orderly shutdown to prevent damage. If the processor enters one of the above power states with PROCHOT# already asserted, PROCHOT# will remain asserted until the processor exits the Stop Grant power state and the processor junction temperature drops below the thermal trip point. If Intel Thermal Monitor automatic mode is disabled, the processor will be operating out of specification. Regardless of mode, in the event of a catastrophic cooling failure, the processor will automatically shut down when the silicon reaches a temperature of approximately 125 C. At this point the THERMTRIP# signal will go active. THERMTRIP# activation is 12 Thermal Design Guide

13 Processor Thermal Features independent of processor activity and does not generate any bus cycles. When THERMTRIP# is asserted, the processor core voltage must be shut down within the time specified in the Intel Atom Processor D510 External Design Specification. The Thermal Monitor consists of the following components: A highly accurate on-die temperature sensing circuit A bi-directional signal (PROCHOT#) that indicates if the processor has exceeded its maximum temperature or can be asserted externally to activate the Thermal Control Circuit (TCC) A Thermal Control Circuit that will attempt to reduce processor temperature by rapidly reducing power consumption when the on-die temperature sensor indicates that it has exceeded the maximum operating point. Registers to determine the processor thermal status Thermal Monitor 2 Note: Intel Atom Processor D410 and D510 support TM1 Intel Atom Processor N450 supports TM1 and TM2 The processor supports an enhanced Thermal Control Circuit. In conjunction with the existing Thermal Monitor logic, this capability is known as Thermal Monitor 2. This enhanced TCC provides an efficient means of reducing the power consumption within the processor and limiting the processor temperature. When Thermal Monitor 2 is enabled, and a high temperature situation is detected, the enhanced TCC will be activated. The enhanced TCC causes the processor to adjust its operating frequency (by dropping the bus-to-core multiplier to its minimum available value) and input voltage identification (VID) value. This combination of reduced frequency and VID results in a reduction in processor power consumption. A processor enabled for Thermal Monitor 2 includes two operating points, each consisting of a specific operating frequency and voltage. The first operating point represents the normal operating condition for the processor. The second operating point consists of both a lower operating frequency and voltage. When the TCC is activated, the processor automatically transitions to the new frequency. This transition occurs very rapidly (to the order of 5 microseconds). During the frequency transition, the processor is unable to service any bus requests, all bus traffic is blocked. Edge-triggered interrupts will be latched and kept pending until the processor resumes operation at the new frequency. Once the new operating frequency is engaged, the processor will transition to the new core operating voltage by issuing a new VID code to the voltage regulator. The voltage regulator must support VID transitions to support Thermal Monitor 2. During the voltage change, it will be necessary to transition through multiple VID codes to reach the target operating voltage. Each step will be one VID table entry (i.e., 12.5 mv steps). The processor continues to execute instructions during the voltage transition. Operation at the lower voltage reduces the power consumption of the processor, providing a temperature reduction. Once the processor has sufficiently cooled, and a minimum activation time has expired, the operating frequency and voltage transition back to the normal system Thermal Design Guide 13

14 Processor Thermal Features operating point. Transition of the VID code will occur first, in order to ensure proper operation once the processor reaches its normal operating frequency. Refer to Figure 3 for an illustration of this ordering. Figure 3. Thermal Monitor 2 Frequency and Voltage Ordering T TM2 Temperature PROCHOT# f MAX f TM2 Frequency VID VID TM2 VID Time 3.3 PROCHOT # Signal The primary function of the PROCHOT# signal is to provide an external indication that the processor has exceeded its maximum operating temperature. While PROCHOT# is asserted, the TCC will be active. Assertion of the PROCHOT# signal is independent of any register settings within the processor. It is asserted any time the processor die temperature reaches the trip point. PROCHOT# can be configured via the BIOS as an output or bi-directional signal. As an output, PROCHOT# will go active when the processor temperature of either core exceeds its maximum operating temperature. This indicates the TCC has been activated. As an input, assertion of PROCHOT# will activate the TCC for both cores. The TCC will remain active until the system de-asserts PROCHOT# As an output, the temperature at which the PROCHOT# signal becomes active is individually calibrated during manufacturing. The power dissipation of each processor affects the set point temperature and once configured in the manufacturing process, the temperature at which the PROCHOT# signal is asserted is not re-configurable. One possible application is the thermal protection of voltage regulators (VR). System designers can create a circuit to monitor the VR temperature and activate the TCC when the temperature limit of the VR is reached. By asserting PROCHOT# (pulled-low) 14 Thermal Design Guide

15 Processor Thermal Features which activates the TCC, the VR can cool down as a result of reduced processor power consumption. Bi-directional PROCHOT# can allow VR thermal designs to target maximum sustained current instead of maximum current. Systems should still provide proper cooling for the VR, and rely on bi-directional PROCHOT# signal only as a backup in case of system cooling failure. Note: A thermal solution designed to meet the thermal specifications should rarely experience activation of the TCC as indicated by the PROCHOT# signal going active. 3.4 Thermal Control Circuit The Thermal Control Circuit portion of the Thermal Monitor must be enabled for the processor to operate within specifications. The Thermal Monitor s TCC, when active, will attempt to lower the processor temperature by reducing the processor power consumption. In the original implementation of thermal monitor this is done by changing the duty cycle of the internal processor clocks, resulting in a lower effective frequency. When active, the TCC turns the processor clocks off and then back on with a predetermined duty cycle. The duty cycle is processor specific, and is fixed for a particular processor. The maximum time period the clocks are disabled is ~3 μs. This time period is frequency dependent and higher frequency processors will disable the internal clocks for a shorter time period. Figure 4 illustrates the relationship between the internal processor clocks and PROCHOT#. Performance counter registers, status bits in model specific registers (MSRs), and the PROCHOT# output pin are available to monitor the Thermal Monitor behavior. Figure 4. Concept of Clocks under Thermal Monitor Control PROCHOT# Normal clock Internal clock Duty cycle control Resultant internal clock Thermal Design Guide 15

16 Processor Thermal Features 3.5 Operation and Configuration To maintain compatibility with previous generations of processors, which have no integrated thermal logic, the Thermal Control Circuit portion of Thermal Monitor is disabled by default. During the boot process, the BIOS must enable the Thermal Control Circuit. Thermal Monitor must be enabled to ensure proper processor operation. The Thermal Control Circuit feature can be configured and monitored in a number of ways. OEMs are required to enable the Thermal Control Circuit while using various registers and outputs to monitor the processor thermal status. The Thermal Control Circuit is enabled by the BIOS setting a bit in an MSR (model specific register). Enabling the Thermal Control Circuit allows the processor to attempt to maintain a safe operating temperature without the need for special software drivers or interrupt handling routines. When the Thermal Control Circuit has been enabled, processor power consumption will be reduced after the thermal sensor detects a high temperature (i.e., PROCHOT# assertion). The Thermal Control Circuit and PROCHOT# transitions to inactive once the temperature has been reduced below the thermal trip point, although a small time-based hysteresis has been included to prevent multiple PROCHOT# transitions around the trip point. External hardware can monitor PROCHOT# and generate an interrupt whenever there is a transition from active-toinactive or inactive-to-active. PROCHOT# can also be configured to generate an internal interrupt which would initiate an OEM supplied interrupt service routine. Regardless of the configuration selected, PROCHOT# will always indicate the thermal status of the processor. The power reduction mechanism of the thermal monitor can also be activated manually using an on-demand mode. Refer to Section 3.6 for details on this feature. 3.6 On-Demand Mode For testing purposes, the Thermal Control Circuit may also be activated by setting bits in the ACPI MSRs. The MSRs may be set based on a particular system event (e.g., an interrupt generated after a system event), or may be set at any time through the operating system or custom driver control thus forcing the thermal control circuit on. This is referred to as on-demand mode. Activating the thermal control circuit may be useful for thermal solution investigations or for performance implication studies. When using the MSRs to activate the on-demand clock modulation feature, the duty cycle is configurable in steps of 12.5%, from 12.5% to 87.5%. For any duty cycle, the maximum time period the clocks are disabled is ~3 μs. This time period is frequency dependent, and decreases as frequency increases. To achieve different duty cycles, the length of time that the clocks are disabled remains constant, and the time period that the clocks are enabled is adjusted to achieve the desired ratio. For example, if the clock disable period is 3 µs, and a duty cycle of ¼ (25%) is selected, the clock on time would be reduced to approximately 1 μs [on time (1 μs) total cycle time (3 + 1) μs = ¼ duty cycle]. Similarly, for a duty cycle of 7/8 (87.5%), the clock on time would be extended to 21 μs [21 (21 + 3) = 7/8 duty cycle]. In a high temperature situation, if the thermal control circuit and ACPI MSRs (automatic and on-demand modes) are used simultaneously, the fixed duty cycle determined by automatic mode would take precedence. 16 Thermal Design Guide

17 Processor Thermal Features 3.7 System Consideration Intel requires the Thermal Monitor and Thermal Control Circuit to be enabled for all processors. The thermal control circuit is intended to protect against short term thermal excursions that exceed the capability of a well designed processor thermal solution. Thermal Monitor should not be relied upon to compensate for a thermal solution that does not meet the thermal profile up to the thermal design power (TDP). Each application program has its own unique power profile, although the profile has some variability due to loop decisions, I/O activity and interrupts. In general, compute intensive applications with a high cache hit rate dissipate more processor power than applications that are I/O intensive or have low cache hit rates. The processor TDP is based on measurements of processor power consumption while running various high power applications. This data is used to determine those applications that are interesting from a power perspective. These applications are then evaluated in a controlled thermal environment to determine their sensitivity to activation of the thermal control circuit. This data is used to derive the TDP targets published in the processor datasheet. A system designed to meet the thermal specification of T JUNCTION-MAX values published in the processor datasheet greatly reduces the probability of real applications causing the thermal control circuit to activate under normal operating conditions. Systems that do not meet these specifications could be subject to more frequent activation of the thermal control circuit depending upon ambient air temperature and application power profile. Moreover, if a system is significantly under designed, there is a risk that the Thermal Monitor feature will not be capable of maintaining a safe operating temperature and the processor could shutdown and signal THERMTRIP#. 3.8 Operating System and Application Software The Thermal Monitor feature and its thermal control circuit work seamlessly with ACPI compliant operating systems. The Thermal Monitor feature is transparent to the application software since the processor bus snooping, ACPI timer, and interrupts is active at all times. 3.9 THERMTRIP# Signal In the event of a catastrophic cooling failure, the processor will automatically shut down when the silicon temperature reaches its operating limit. At this point the system bus signal THERMTRIP# becomes active and power must be removed from the processor. THERMTRIP# activation is independent of processor activity and does not generate any bus cycles. Refer to the processor datasheet for more information about THERMTRIP#. The temperature at which the THERMTRIP# signal becomes active is individually calibrated during manufacturing. The temperature at which THERMTRIP# becomes active is roughly parallel to the thermal profile and greater than the PROCHOT# activation temperature. Once configured, the temperature at which the THERMTRIP# signal is asserted is neither re-configurable nor accessible to the system. Thermal Design Guide 17

18 Processor Thermal Features 3.10 Cooling System Failure Warning It may be useful to use the PROCHOT# signal as an indication of cooling system failure. Messages could be sent to the system administrator to warn of the cooling failure, while the thermal control circuit would allow the system to continue functioning or allow a normal system shutdown. If no thermal management action is taken, the silicon temperature may exceed the operating limits, causing THERMTRIP# to activate and shut down the processor. Regardless of the system design requirements or thermal solution ability, the Thermal Monitor feature must be enabled to ensure proper processor operation Digital Thermal Sensor The Intel Atom Processors N450, D410 and D510 introduce the Digital Thermal Sensor (DTS) as the on-die sensor to use for processor temperature monitoring. The Processor will have both the DTS and thermal diode enabled. The DTS monitors the same sensor that activates the TCC (see Section 3.4). The readings from the DTS are relative to the activation of the TCC. The DTS value where TCC activation occurs is 0 (zero). The Intel Atom processors DTS can only be accessed via an MSR. The value read via the MSR is an unsigned number of degrees C away from TCC. Multiple digital thermal sensors can be implemented within the package without adding a pair of signal pins per sensor as required with the thermal diode. The digital thermal sensor is easier to place in thermally sensitive locations of the processor than the thermal diode. This is achieved due to a smaller foot print and decreased sensitivity to noise. Since the DTS is factory set on a per-part basis there is no need for the health monitor components to be updated at each processor family Thermal Diode The processor incorporates an on-die PNP transistor whose base emitter junction is used as a thermal diode, with its collector shorted to ground. The thermal diode can be read by an off-die analog/digital converter (a thermal sensor) located on the motherboard or a stand-alone measurement kit. The thermal diode may be used to monitor the die temperature of the processor for thermal management or instrumentation purposes but is not a reliable indication that the maximum operating temperature of the processor has been reached. When using the thermal diode, a temperature offset value must be read from a processor MSR and applied. The reading of the external thermal sensor (on the motherboard) connected to the processor thermal diode signals will not necessarily reflect the temperature of the hottest location on the die. This is due to inaccuracies in the external thermal sensor, on-die temperature gradients between the location of the thermal diode and the hottest location on the die, and time based variations in the die temperature measurement. Time based variations can occur when the sampling rate of the thermal diode (by the thermal sensor) is slower than the rate at which the TJ temperature can change. Offset between the thermal diode based temperature reading and the Intel Thermal Monitor reading may be characterized using the Intel Thermal Monitor s Automatic mode activation of the thermal control circuit. This temperature offset must be taken 18 Thermal Design Guide

19 Processor Thermal Features into account when using the processor thermal diode to implement power management events. This offset is different than the diode Toffset value programmed into the Intel Atom processor Model Specific Register (MSR). Table 3 and Table 4 provide the diode interface and specifications. The transistor model parameters shown in Table 4 provide more accurate temperature measurements when the diode ideality factor is closer to the maximum or minimum limits. Contact your external sensor supplier for their recommendation. The thermal diode is separate from the Thermal Monitor s thermal sensor and cannot be used to predict the behavior of the Thermal Monitor. Table 3. Thermal Diode Interface Signal Name Pin/Ball Number Signal Description THERMDA_1 D30 Thermal diode anode THERMDA_2 C30 Thermal diode anode (on D510 only) THERMDC_1 E30 Thermal diode cathode THERMDC_2 D31 Thermal diode anode (on D510 only) Table 4. Thermal Diode Parameters using Transistor Model Symbol Parameter Min Typ Max Unit Notes IFW Forward Bias Current μa 1 IE Emitter Current μa 1 nq Transistor Ideality ,3,4 Beta ,3 RT Series Resistance Ω 2,5 NOTES: 1. Intel does not support or recommend operation of the thermal diode under reverse bias. 2. Characterized across a temperature range of C. 3. Not 100% tested. Specified by design characterization. 4. The ideality factor, nq, represents the deviation from ideal transistor model behavior as exemplified by the equation for the collector current: IC = IS * (e qvbe/nqkt 1) where IS = saturation current, q = electronic charge, VBE = voltage across the transistor base emitter junction (same nodes as VD), k = Boltzmann Constant, and T = absolute temperature (Kelvin). 5. The series resistance, RT, provided in the Diode Model Table (Table 4) can be used for more accurate readings as needed. When calculating a temperature based on the thermal diode measurements, a number of parameters must be either measured or assumed. Most devices measure the diode ideality and assume a series resistance and ideality trim value, although are capable of also measuring the series resistance. Calculating the temperature is then accomplished using the equations listed under Table 4. In most sensing devices, an expected value for the diode ideality is designed into the temperature calculation equation. If the designer of the temperature sensing device assumes a perfect diode, the ideality value (also called ntrim) will be Given that most diodes are not perfect, the designers usually select an ntrim value that more closely matches the behavior of the diodes in the processor. If the processor diode ideality deviates from Thermal Design Guide 19

20 Processor Thermal Features that of the ntrim, each calculated temperature will be offset by a fixed amount. This temperature offset can be calculated with the equation: Terror(nf) = Tmeasured * (1 - nactual/ntrim) where T error(nf) is the offset in degrees C, T measured is in Kelvin, n actual is the measured ideality of the diode, and n trim is the diode ideality assumed by the temperature sensing device. 20 Thermal Design Guide

21 Thermal Solution Requirement 4 Thermal Solution Requirement 4.1 Characterizing the Thermal Solution Requirement The idea of a thermal characterization parameter, Ψ (Greek letter Psi), is a convenient way to characterize the performance needed for the thermal solution and to compare thermal solutions in identical situations (i.e., heating source, local ambient conditions, etc). A thermal characterization parameter is calculated using total package power, whereas actual thermal resistance, Θ (theta), is calculated using actual power dissipated between two points. Measuring actual power dissipated into a heatsink is difficult, since some of the power is dissipated via heat transfer into the package, board and surrounding air. The junction-to-local ambient thermal characterization parameter (Ψ JA ) is used as a measure of the thermal performance of the overall thermal solution. It is defined by the following equation, and measured in units of C/W: Equation 4-1. Junction- to- Local Ambient Thermal Charaterization Parameter (Ψ JA ) Where: Ψ JA TJ = MAX T TDP Ψ JA =Junction-to-local ambient thermal characterization parameter ( C/W) T J- MAX = Maximum allowed device temperature ( C) T LA = Local ambient temperature near the device ( C) TDP=Thermal Design Power (W), assumes all power dissipates through the top surface of the device. The junction-to-local ambient thermal characterization parameter, Ψ JA, comprises Ψ JS, which includes the thermal interface material thermal characterization parameter, and Ψ SA, the sink-to-local ambient thermal characterization parameter. LA Thermal Design Guide 21

22 Thermal Solution Requirement Equation 4-2. Junction- to- Local Ambient Thermal Charaterization Parameter Ψ JA =Ψ JS + Ψ SA Where: Ψ JS = Thermal characterization parameter of the package and TIM ( C/W) Ψ SA = Thermal characterization parameter from heatsink-to-local ambient ( C/W) Ψ JS is strongly dependent on the thermal conductivity and thickness of TIM between heatsink and die. Ψ SA is a measure of the thermal characterization parameter from the geometric center of the heatsink base to the local ambient air. Ψ SA depends on the heatsink material, thermal conductivity, and geometry. It is also depends strongly on the air velocity through the fins of the heatsink. As the ambient temperature increases, the required Ψ SA decreases, hence the heatsink dimension increases or the airflow needs to be increased so that the thermal solution target performance can be met. Figure 5 illustrates the combination of the different thermal characterization parameters. Figure 5. Processor Thermal Characterization Parameter Relationships T A Heatsink Ψ SA Ψ JA TIM T S Ψ JS PCB Device T J 22 Thermal Design Guide

23 Thermal Solution Requirement 4.2 Example: Calculating the Required Thermal Performance The process to determine the required thermal performance needed to cool the device includes: Define a target component temperature T J-Max and corresponding TDP Define a target local ambient temperature T LA Use Equation 4-1. and Equation 4-2 to determine the required thermal performance needed to cool the device The following example illustrates how to determine the appropriate performance targets: Assume: TDP= 15.0W and T J-MAX = 100 C (Available from processor datasheet) Local processor ambient temperature, T LA =35 C Then the following could be calculated using Equation 4-1 for the given processor frequency: TJ MAX TLA o ΨJA = = = 5 C / W TDP 13 W To determine the required heatsink performance, a heatsink solution provider would need to determine Ψ JS performance for the selected TIM and mechanical load configuration. If the heatsink solution were designed to work with TIM material performing at Ψ JS 0.55 C/W solving from Equation 4-2, the performance of the heatsink required is: Ψ SA = Ψ JA Ψ JS = 5.0 (0.55) = 4.45 C W o If the local processor ambient temperature is increased to 40 C, the same calculation can be carried out to determine the new thermal solution performance requirement. TJ MAX TLA o ΨJA = = = 4.6 C / W TDP 13 It is evident from the above calculations that an increase in the local ambient temperature has a significant effect on the junction-to-ambient thermal resistance requirement. This effect can increase cost, heatsink size, heatsink weight, or a higher system airflow rate. Table 5 summarizes the thermal budget required to adequately cool the processor. Since the data is based on air data at sea level, a correction factor would be required to estimate the thermal performance at other altitudes. Thermal Design Guide 23

24 Thermal Solution Requirement Table 5. Required Thermal Solution Performance (Ψ JA ) SKU, TDP Ψ JA (ºC/W) at T LA = 35ºC 1,2 Ψ JA (ºC/W) at T LA = 55ºC 1,2 Intel Atom processor N450, 5.5 W Intel Atom processor D410, 10W Intel Atom processor D510, 13W T LA is defined as the local (internal) ambient temperature measured approximately 1 upstream from the device. 2. Ψ JA is determined by (T J-MAX T LA )/TDP, so this value will change if any parameter changes. 24 Thermal Design Guide

25 Reference Thermal Solution 5 Reference Thermal Solution 5.1 Thermal Solution Design Considerations The thermal solution in a fanless system can be placed into two general categories: stand-alone natural convection heatsink and conduction cooling system. A stand-alone natural convection heatsink is similar to a typical, extruded heatsink. The heatsink contacts only the component that it is cooling. This thermal solution is placed inside the chassis and relies on natural air movement created by a temperature difference instead of forced convection from an airflow source to remove the heat. A conduction cooled system is one in which the heat dissipating component(s) are attached to the chassis and rely on a majority of the heat being conducted into the chassis. This type of solution relies on natural convection to remove heat from the chassis. In this case, the heat dissipating components are usually directly attached to the chassis or utilize a heatpipe to transfer the heat to the chassis. The next section explains the major factors that influence a fanless thermal solution design. 5.2 Thermal Solution Design Factors 1. Thermal design power (TDP) and ambient temperature: The TDP for a component is probably the biggest factor in determining whether a component can be cooled in a fanless system. In most cases, a target power for fanless cooling is less than 10 W, but this depends on the target ambient temperature. Intel Atom processors N450, D410 and D510 are good candidates for fanless cooling even though the power is slightly above 10 W. 2. The area of the surface on which the heat transfer takes place: Without enhancements, this is the surface of the processor (bare die). One method to improve thermal performance to attach a heatsink to the bare die. A heatsink can increase the effective heat transfer surface area by conducting heat from the die and into the surrounding air through fins attached to the heatsink base. 3. The conduction path from the heat source to the heatsink fins: Providing a direct conduction path from the heat source to the heatsink fins and selecting materials with higher thermal conductivity typically improves heatsink performance. The length, thickness, and conductivity of the conduction path from the heat source to the fins directly impact the thermal performance of the heatsink. In particular, the quality of the contact between the die surface and the heatsink base has a greater impact on the overall thermal solution performance as processor cooling requirements become stricter. 4. Thermal Interface Material (TIM): TIM fills the gap between die and the bottom surface of the heatsink, improving the overall performance of the stackup (TIM-heatsink). With an extremely poor heatsink interface flatness or roughness, the TIM may not adequately fill the gap. The TIM thermal Thermal Design Guide 25

26 Reference Thermal Solution performance depends on its thermal conductivity and the pressure applied to it. 5. Heat Distribution: In the case of conduction cooled system thermal solutions, it is important to optimize the heat distribution from heat source(s). This can be achieved by using multiple heatpipes to transport the heat to a larger area of the system chassis. 6. Fin thickness and fin pitch: In a natural convection solution, the air flow is induced by the phenomenon of hot air moving to the opposite of gravitational direction. Therefore, the fin to fin spacing and the thickness of the fins play a critical role in improving the air flow and reducing thermal resistance. Thermal solution designers need to optimize these parameters to obtain the best performance while designing for manufacturability. 7. Location of venting in the chassis: The vents in the chassis allow for heat to escape and for external air that is at a lower temperature to enter the chassis. Critical components with the highest amount of power generation (usually the processor) need to be placed close to the chassis vents. This placement facilitates the movement of air caused by thermodynamic effects. 8. Heat trapped inside fully enclosed system: For fanless systems that are fully enclosed, not all heat sources have direct heat conduction to the heatsink(s) or chassis. Therefore, the heat generated could eventually lead to internal heat accumulation until system failure results due to raising the internal local ambient temperature (TLA). System thermal solution designers must take into account this potential impact to temperature inside the chassis. 9. Maximum allowable chassis temperature: The external chassis temperature should be considered in applications where a fanless system will have potential users come in contact with the chassis. Due to the amount of heat transfer to the outer chassis there is potential for the surface to burn a user who comes in contact with the device. System designers need to monitor the surface temperature of the chassis to ensure that end users will not be harmed and the chassis temperature meets applicable standards To analyze all these design factors it is recommended that designers utilize third-party CFD thermal analysis software such as Flotherm* and Icepak*. Intel has package models for the Intel Atom processors N450, D510 and D510 product line available for these software packages. Contact your Intel Field representative for more information. 5.3 Natural Convection Heatsink Experimental Test Setup Intel has developed reference thermal solutions that are suitable for the Intel Atom processor in natural convection environments. These heatsinks were tested in a test chamber as shown in Figure 6. These tests were performed on the component level to characterize the performance of the heatsink. System designers will have to use this performance data apply it to their system design, which is best achieved through CFD computer simulations. 26 Thermal Design Guide